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Technical Analysis on Energy Saving of Frequency Converters
As an advanced energy-saving technology, inverter technology has been popularized and applied for many years. Inverters are also widely used in various aspects of industry and civil use. But does it really save energy after using the inverter? People often feel differently!
Viewpoint 1: Some people say that the inverter air conditioner is installed in my house, but it does not save electricity, and even consumes more electricity. So the inverter does not save energy.
Viewpoint 2: Some people say that the water pump of the chiller in our factory has been transformed with frequency conversion, and the energy saving effect is very obvious. So the inverter can save energy.
Viewpoint 3: It seems that frequency converter speed regulation can save power, but because the frequency converter is not efficient, and the efficiency of the motor will also decrease at low speed, the frequency converter does not save energy. Moreover, the cost of configuring the frequency converter is high, even if it can save a little electricity, it is not economically cost-effective as a whole.
First, let's take a look at the basic principle of the inverter:


Frequency converters are usually used in fans, pumps, compressors and other equipment, and the medium is fluid. According to the principle of fluid mechanics, when the induction motor drives a load such as a water pump, the flow Q is proportional to the motor speed n, the pressure H is proportional to the square of the motor speed n, and the relationship between the actual power of the motor and the flow and pressure is P∝QxH, that is, the power Proportional to the 3rd power of the rotational speed. For example, when the motor speed is reduced to 0.8 times the rated speed, the power consumed by the motor will be reduced to 0.83=0.512 times the rated power. It can be seen that the use of frequency conversion technology can greatly save energy. Let's take a look at the process of energy transfer:


energy transfer process


Based on this theory, let's look back at the several viewpoints mentioned earlier:


Viewpoint 1: Some people say that the inverter air conditioner is installed in my house, but it does not save electricity, and even consumes more electricity. So the inverter does not save energy.


Analysis: According to the above analysis, the premise of inverter energy saving is that the load is small and the motor speed slows down. The inverter air conditioner at home does not save energy because the load does not become smaller at all, and the compressor always runs at a higher speed. For example, under the same climate conditions, if a 10-square-meter room is equipped with 3-hp air conditioners, the air-conditioning will not operate at full capacity, and the inverter air conditioner will definitely save energy; if a 100-square-meter room is also equipped with 3-hp inverter air conditioners, it will definitely not save energy. , because the air conditioner is always running at full capacity. It can only be said that when air conditioner manufacturers claim that inverter air conditioners are energy-saving, they do not make it clear under what circumstances they save energy. Do you feel cheated?


Viewpoint 2: Some people say that the water pump of the chiller in our factory has been transformed with frequency conversion, and the energy saving effect is very obvious. So the inverter can save energy.


Analysis: Usually in industrial design, there is a relatively large margin for loads such as fans and pumps, and in most cases, the operating load is low. Under such a premise, the frequency conversion energy-saving technology has a lot of energy-saving space. However, the transformation of the inverter should be based on the operation of the specific project, and a technical and economic comparison should be carried out. Simply put, how long will it take for the initial investment in new construction or renovation to pay off through the frequency converter energy-saving technology.


Viewpoint 3: It seems that frequency converter speed regulation can save power, but because the frequency converter is not efficient, and the efficiency of the motor will also decrease at low speed, the frequency converter does not save energy. Moreover, the cost of configuring a frequency converter is relatively high, and even if it can save a little electricity, it is not economical in terms of the overall situation.


Analysis: This point of view is considered comprehensive, from the perspective of energy saving of the entire system, considering the efficiency issue. However, what I want to say is that the efficiency of frequency converters may be higher than imagined. Now the technology of mainstream frequency converters can usually reach 0.9 or more. When the motor reduces the speed, the efficiency drops, but the energy consumption is three times according to the speed. ratio decreased. It can be said that inverter technology is still energy efficient when considering the efficiency of the inverter and the motor. Of course, the premise is that there is a premise of reducing the load operation.


As for whether the overall economy is cost-effective, we can only make technical and economic comparisons for specific projects.


Thinking: The inverter energy-saving technology is a relatively mature technology, but whether all loads and all operating conditions are suitable for configuring inverters, the answer is no. We still have to make technical and economic comparisons on a case-by-case basis. In fact, the inverter has multiple functions, such as speed regulation, soft start, voltage regulation, etc. Energy saving is only a function brought by speed regulation, and don't "forget it".